1. Field of the Invention
The present invention relates to a data management system for managing digital data, and in particular to a system which can be applied to copyright management of copyrighted data, electronic commerce, and digital cash.
2. Background Art
As database systems store increasingly larger amount of information, database systems are becoming popular in which many computers, used to store various types of data independently, are connected via communication lines to share the data.
In such a database system, the information handled up to this point has been conventionally coded information that can be processed by a computer, and that contains a relatively small amount of information and monochrome binary data, such as facsimile information at most. And it was not possible to handle data containing a relatively large amount of information, such as data for natural pictures or animation. A technique is under development for digital processing of picture signals other than binary data which were handled only as analog signals in the past.
By digitizing the picture signal, it is possible to handle a picture signal, e.g., a television signal, by a computer. "Multimedia systems" is an emerging technology of the future capable of simultaneously handling the data handled by computers and digitized picture data.
Because picture data contains a much larger amount of information compared with character data and audio data, it is difficult to store or transfer or process the picture data by computer. For this reason, techniques for compressing or expanding picture data have been developed. Further, several standards for compression/expansion of picture data have been established. For example, the following standards have been established as common standards: JPEG (Joint Photographic image coding Experts Group) standards for still pictures, H.261 standards for video conferences, MPEG1 (Moving Picture image coding Experts Group 1) standards for picture accumulation, and MPEG2 standards for current television broadcasting and high definition television broadcasting. These new techniques have made it possible to process digital picture data in real time.
For analog data, which has been widely used in the past, the control of copyrights during processing has not been an important issue because the quality of the analog data degrades each time the data is stored, copied, edited, or transferred. However, the quality of digital data does not degrade when the data is repeatedly stored, copied, edited, or transferred. Therefore, the management and control of copyrights during processing of digital data is an important issue.
In the past, there has been no adequate method for management and control of copyrights for digital data. It has been managed and controlled merely by copyright law or by contracts. In copyright law, only compensation for digital sound or picture recording devices has been prescribed.
It is possible not only to refer to the content of a database, but also to effectively utilize the data obtained from the database by storing, copying, or editing the data, and also transferring the edited data to the database with the edited data registered as new data. Further, it is possible to transfer edited data to other persons via an on-line means such as a communication link or via an off-line means such as a proper recording medium.
Conventional database system have dealt with only character data. However, in multimedia systems, sound data and picture data originally generated as analog data, are digitized and included in the database in addition to the other data in the database such as character data.
Under such circumstances, it is important to control copyrights of the data in the database. However, none of the prior art methods provides a complete copyright management and control for such operations as copying, editing, transferring, etc. of data.
In the past, computers have been used in relatively small scale for data communication. Computer communication system called "Internet" has shown a rapid progress in the past several years, and it is now being developed to a system closer and familiar to everybody. The information used in communication of this Internet system has been initially limited to character information only, but, with the progress of technique, audio data and picture data are now used. At present, even electronic commerce data or digital cash data, for which reliability and confidentiality are important factors, are now being used in the Internet system.
Under such circumstances, it has become necessary to establish new techniques to ensure and guarantee security to keep confidentiality and reliability of the processed data and also of the case where it is necessary to charge and collect fee.
In the information data, i.e. copyrighted data, for which fee is charged when utilizing such data, copyright is asserted in most cases, while there are information data such as personal mail, advertisement and propaganda data, etc., for which copyright is not positively asserted. For example, in case of a personal mail, for which copyright is not asserted, it is important to maintain privacy and to prevent falsification or forgery of the contents. Even in the data for advertisement and propaganda, which is usually not associated with assertion of copyright, damage or impairment may often occur due to falsification of the contents or business activities may be disturbed because of distribution of the data to the people other than those originally aimed or such trouble may be caused by false data.
As described above, it is essential in case of personal mail to stop falsification of contents, to prevent infringement of privacy and to exclude forgery. For the advertisement and propaganda data, it is necessary to prevent falsification of data contents, to restrict looking and to exclude forgery.
The prevention of infringement of privacy in the personal mail and the restriction of looking of the advertisement and propaganda data can be achieved by encryption of data. The prevention of forgery of the personal mail and the advertisement and propaganda data and the exclusion of falsification of the personal mail and the advertisement and propaganda data can be attained by confirmation (certification) of the sender or the transmitter of the data.
The Internet system is based on grass-roots concept and is a very fragile system as far as security of the system itself is concerned. Various systems for maintaining security of the Internet system have been proposed, and typical systems are PEM (Privacy Enhanced Mail) adopting hierarchical structure and PGP (Pretty Good Privacy) adopting horizontal distributed structure. These systems are effective to maintain confidentiality of data and to provide certification of the transmitting source, certification on non-falsification of the data, display of the first transmitter and control of public-key, while it is not possible by these systems to restrict re-utilization of data including data editing.
PEM, adopting hierarchical structure, comprises the most upper-level authority called IPRA (Internet PCA Registration Authority), a next upper-level authority called PCA (Policy Certification Authority), and the most lower-level authorities called Organizational, Residential and Personal respectively. Upper-level certification authorities issue a public-key certificate with digital signature on the data such as name of the lower-level auhority for public-key of the lower-level authority, thus guaranteeing validity of the public-key.
PGP, adopting horizontal distributed structure, has no entity to correspond to the certification authority of PEM, and a reliable third person guarantees validity of the public-key by issuing a public-key certificate with digital signature to the data such as name of the public-key. In this PGP, there is a method called electronic fingerprinting to easily confirm the public-key. By this method, the public-key is hashed by one-way hash function such as MD 5 (Message Digest 5), and 16-byte hash value is confirmed by voice.
When PEM is compared with PGP, there is no problem on the certifier in PEM, which adopts hierarchical structure, but this is not necessarily a commonly used system in the Internet System, which is based on grass-roots concept. On the other hand, PGP is a simplified system, which can be widely used. However, this cannot be utilized in case there is no reliable person to sign.
With recent development of computer network system, individual computers, used on stand-alone basis in the past, are connected together through the network system, and database system to commonly share the data is now propagated. Further, distributed object system has been proposed, in which application program or basic software called operating system as well as data is also commonly shared through the network.
In the distributed object system, both data and software are supplied by a server as an object, which comprises program and data. In the distributed object system, there are two systems, i.e. a system called object container, in which operating system, application program and data are provided by a server and data processing and data storage are performed by a user terminal unit, which is an ordinary computer, and a system called server object, in which operating system, application program and data are provided by a server, and data processing is performed by a user terminal unit called network computer, while data storage is carried out by a server. The server object system is further developed to a system, in which data processing is also performed by the server, and the user terminal unit is provided only with input/output function, and the whole system functions as a single computer.
Another form of the network system called "license network" as rental network system, is considered. In this system, an enterprise providing network base such as communication lines also provides the systems other than communication lines such as fee charging system, security system, copyright management system, certification system, etc. And a service enterprise utilizes these services and carries out network business as if it is his own system.